1. Field of the Invention
The present invention relates to a magnetoresistance effect element, a magnetoresistance effect type head and a magnetic recording/reproducing apparatus and, more particularly, to a magnetoresistance effect element containing an antiferromagnetic layer, a magnetoresistance effect type head using such a magnetoresistance effect element and a magnetic recording/reproducing apparatus using also the same element.
2. Description of the Related Art
Some of magnetoresistance effect elements used for a magnetoresistance effect type head include an antiferromagnetic layer that exhibits exchange coupling with a magnetic layer.
FIG. 10 shows a structure of a spin valve element (a sensor device of a spin valve head) defined as one of the element described above. As shown in FIG. 10, the spin valve element has such a configuration that a free layer 32, an intermediate layer 33, a pinned layer 34 and an antiferromagnetic layer 35 are laminated on a base material 31. Among those layers, the free layer 32 and the pinned layer 34 are composed of a ferromagnetic material (normally, NiFe (Nickel/Iron) alloy; Permalloy) exhibiting a small anisotropic magnetic field, and the intermediate layer 33 is formed by use of a non-magnetic metal such as Cu (copper). Then, the antiferromagnetic layer 35 involves the use of a layer composed of an antiferromagnetic material which proudes a strong exchange coupling with the pinned layer 34 by its coming into tight contact at an atomic level with the pinned layer 34. The exchange coupling provides the spin valve element with an excellent magnetic field detecting characteristic.
Known also is a magnetoresistance effect element including a single magnetic layer and the antiferromagnetic layer.
It is taken for granted that the material for forming the antiferromagnetic layer of the magnetoresistance effect element having the construction described above is required to produce the strong exchange coupling with the magnetic layer (to increase a coupling magnetic field between the magnetic layer and the antiferromagnetic layer to be formed). In addition, the above material is required to exhibit a high anticorrosion and a high thermal stability as well as to be easy to form the antiferromagnetic layer.
The materials (FeMn, IrMn, RhMn, NiO, NiMn, PtMn etc) hitherto used for forming the antiferromagnetic layer have defects in some points in terms of serving as the materials for the antiferromagnetic layer. For example, NiMn and PtMn do not exhibit a desired characteristic in an as-layer-formed state. Therefore, in the case of using those materials, it is required that a thermal treatment be effected at a high temperature (approximately 300.degree. C.) after forming the layers. As a result, there arises a problem in which a manufacturing process of the magnetoresistance effect element becomes intricate, and the magnetoresistance effect element exhibiting a uniform characteristic is hard to obtain. Further, NiO exhibits the antiferromagnetic characteristic in the as-layer-formed state and also possesses a high anticorrosion characteristic but is poor in terms of the thermal stability. Another problem inherent in NiO is that a NiO layer exhibits, when being formed thinly, small coupling magnetic field with respect to the magnetic layer.
FeMn, IrMn and RhMn exhibit the antiferromagnetic characteristic in the as-layer-formed state and a comparatively high thermal stability as well, but presents such a problem that the anticorrosion in a composition for producing the strong exchange coupling with a ferromagnetic layer is poor. Hence, according to a technology disclosed in, e.g., Japanese Patent Application Laid-Open Publication No. 8-249616, when forming the antiferromagnetic layer of the spin valve element, there is used an IrMn binary antiferromagnetic material having such a composition (a percentage content of Ir is 30-45% by atom) that the coupling magnetic field to a NiFe magnetic layer is approximately 1/2of the maximum coupling magnetic field that can be actualized by the IrMn binary system antiferromagnetic material.
Further, according to the above Publication, although a magnitude of the coupling magnetic field obtained is reduced by adding Pt, Ru and Rh to IrMn, it is reported that the anticorrosion can be enhanced. To be specific, it is reported that when d=5 in the antiferromagnetic material expressed by (Mn.sub.60 Ir.sub.40).sub.100-d Pt.sub.d (the suffix represents % by atom), though the coupling magnetic field becomes smaller than Mn.sub.6o Ir.sub.40, it exhibits a more excellent anticorrosion than the anticorrosion Mn.sub.6o Ir.sub.40. Then, the same result is to be obtained by use of Ru, Rh in place of Ir.
Thus, according to the technology disclosed in this Publication, the ternary alloy acquired by adding a third element to the IrMn binary alloy in order to enhance the anticorrosion. As a result of being the ternary alloy, however, the coupling magnetic field decreases. Consequently, the ternary alloy disclosed in the above Publication is not suitable as the antiferromagnetic layer material of the magnetoresistance effect element. if the anticorrosion characteristics are enhanced on the assumption that the magnitude of the coupling magnetic field is allowed to decrease, it is desirable that the same magnitude of the coupling magnetic field as in the case of using a certain binary alloy be obtained from the ternary alloy when this ternary alloy is used for the antiferromagnetic layer, and besides it should exhibit the better anticorrosion characteristics than the binary alloy.